1. Field of the Invention
The present invention relates to a high efficiency spark ignition two-stroke cycle internal combustion engine which assures stable and excellent combustion over a wider engine operating region, and provides a lowered amount of hydrocarbon in the exhaust.
2. Description of the Background Art
In general, a two-cycle internal combustion engine executes twice the combustion in the same number of revolutions as a four-cycle internal combustion engine. The two-cycle engine thereby obtains almost twice the output as a four-cycle engine for the same stroke and volume. Therefore, the two-cycle internal combustion engine can provide a high output even with a small size, and it can be manufactured at a low cost with a small number of parts. As a result, the two-cycle engine is particularly suited for powering for vehicle. However, since exhaustion and scavenging in the two-cycle engine are executed simultaneously at a certain period, blow-by is easily generated, and a large amount of hydrocarbon is exhausted. Further, fuel consumption is bad.
An internal combustion engine described in Japanese Patent No. 2,515,276 has solved the problem explained above. In this internal combustion engine, a sub-combustion chamber is provided, and a fuel holding apparatus is provided adjacent to the sub-combustion chamber. The fuel holding chamber of the fuel holding apparatus is always filled with pressurized air compressed up to a predetermined pressure. A predetermined amount of fuel is supplied from a fuel metering apparatus corresponding to the operating condition of the internal combustion engine for a single revolution of the crankshaft. A switching valve of the fuel holding apparatus is opened at the predetermined crank angle and the predetermined amount of fuel in the fuel holding chamber is injected into the sub-combustion chamber together with the compressed air.
In the internal combustion engine explained above, since the fuel holding apparatus is provided adjacent to the sub-combustion chamber, the fuel holding apparatus is subjected to a high temperature. High temperature fuel in the fuel holding apparatus is carbonized when it is in contact with the aperture of the switching valve, and thereby soot adheres to the aperture.
Moreover, a switching valve is provided at the bottom part of the fuel holding chamber. When the switching valve is closed, the fuel collects at the bottom part of the fuel holding chamber. Therefore, when the switching valve is opened, the fuel collected in the bottom part of the fuel holding chamber is released into the sub-combustion chamber. As a result, the highly concentrated mixed air is easily exhausted from an exhaustion hole in the initial condition of the opening of the switching valve. The ability to control the exhaustion of hydrocarbon is lowered, and sufficient improvement of fuel consumption cannot be expected. This tendency is particularly great during a high output condition of the engine.